The invention relates to a method for automatically loading a double-sided polishing machine with wafer crystals.
The manufacture of microelectronic components of a high integration density makes extreme requirements to the level of evenness, non-defectiveness, and roughness of manufactured wafer crystals. The last processing step is the polishing of the wafer crystal after it underwent grinding before. The requirements described are satisfied best by polishing the wafer crystal on either side. A so-called double-sided polishing machine is employed for this purpose.
A double-sided polishing machine is described in DE 195 47 086, for example. It features the fact that the wafer crystal lie in respective reception openings of so-called runner disks. The runner disk, in turn, lies on a lower polishing plate to which a polishing cloth is pasted. The runner disks are set moving and kept moving by means of a roll-off device. An upper polishing plate (to which a polishing cloth is pasted) is caused to travel onto the wafer crystals and double-sided polishing is performed by rotating the polishing plates while adding polishing agents.
The aforementioned document also describes how to bring the runner disks to a predetermined loading and unloading position. Runner disks usually have teeth at the circumference with inner and outer toothed or pinned rims. When the inner and/or outer toothed rim is set into rotation, the runner disks, in turn, are set into rotation while simultaneously moving about the vertical axis of the machine. Since the transmission ratios are known, a positioning drive allows each runner disk to be moved to in a desired position relative to a stationary point (the loading and unloading position).
From DE 100 07 389, it is further known to remove the wafer crystals from the double-sided polishing machine by means of an apparatus. The known device provides a suction head with a plurality of suction apertures by which all wafer crystals in a runner disk can be grasped at the same time. To this end, the suction head is rotatably supported about a vertical axis and may be brought into a rotary position in which the wafer crystals can be simultaneously grasped because of suction.
The double-sided polishing described for wafer crystals is a so-called batch process. It requires that a major number of wafer crystals be placed in the runner before the process starts. It is important for the production lines that the wafer crystals be positioned accurately and with no damaged edges in the correct order and without coming to float. Currently, insertion is by hand and involves the risk of the order not being observed, the edges getting damaged, and one or more wafer crystals coming to float at the beginning of the roll-off rotation and causing damage within the machine. The wafer crystals and the polishing cloth as well as the runner disks may be destroyed and provoke major damage and a production failure.
After the wafer crystals are unloaded, the double-sided polishing machine is rinsed to eliminate polishing agent residues and to keep the polishing cloth and runner disks wet. Polishing agents, when dried in place, involve the hazard of scratches during polishing. The rinsing operation soaks the cloth with water and results in water being trapped in the reception openings or nests. This water possibly leads to crystal floating as described with the undesirable consequences.
It is the object of the invention to describe a method for automatically loading wafer crystals into double-sided polishing machines of the type mentioned at the beginning which avoids damage to the edges and prevents the wafer crystals from floating. Moreover, it is intended to ensure that a predetermined order of the wafer crystals be observed.